Adjustable coupling system



Dec. 5, 1939. A. cRossLEY ADJUSTABLE COfiPLING SYSTEM Filed Aug. 12, 1937 ATTORNEY ES PATENT OFFICE anmsranm COUPLING srs'nm Alired Crossley, Chicago, Ill., assignor to John'- son Laboratories, Inc., Chicago 111., a corporation of Illinois Application August 12, 1937, Serial No. 158,695

9 Claims. (01. 178-44) 1111s invention relates to electrical systems and more particularly to-system's in which it is desirable or necessary to provide for varying the degree of coupling between two or more circuits or networks. The invention'is especially adapted to those cases in which it'is preferable to .vary the coupling without producing any other appreciable change in the conditions in the system. As is well known, if the coupling between two ductivelinkage between them, there is an accompanying alteration in the inductive reactances in each 01 the networks which may untavorably aiiect their performance. The present invention provides means by which the otherwise unavoidable alterations in the coupled networks may be avoided. a

In one common type of high-frequency coupling device for example, in which a pair of resonant circuits is employed, the inductive coupling between the circuits is varied by changing the relative positions of the coils. In the case connecting leads has a definite minimum valuewhich must be taken into account. Thus the attainment of the desired degree of coupling benetworks is varied merely by adjusting the 'in-- Additionally, the catween the circuits in such a coupling device is diilicult, and variation of the coupling over a desired range of values is almost impossible oi as realization in a commercially practical device.

Coupling devices of the type associated with pairs of resonant circuits are usually operated at or somewhat above critical coupling. If the individual resonant circuits are highly emcient,

- 40 the degree of coupling is relatively low and a small change in it produces a marked change in the performance of the device. Previously known devices of this type have not been capable of providing a smooth variation of coupling over the desired narrow but highly important range.

actu'istic o! the device was asymmetrical over at least a portion of the rangeof coupling varia- In the intermediate-frequency amplifiers of receivers of the superhet-erodyne type; the problem of adjusting the coupling without disturbing 5 the conditions in the individual circuits is of particular importance because such a variation incoupling may be utilized to adjust the band width 01 the-amplifier, that is, the range of musical or voice modulation'irequencies which 10 will be passed through to the loud speaker. Several methods 01' altering the band width of such amplifiers have already been proposed, but the present invention provides a new, simple and highly efiective solution of the problem. 15

It is an object of this invention to provide a coupling means which is capable of precise coupling adjustment without affecting the total efiective inductance of the circuits with which it may be employed.

-It is an additional object of the invention to provide means whereby both the sense and the degree of inductive coupling between two circuits or networks may be varied without influencing the effective inductance values in either of the circuits or networks.

In accordance with the-invention, these and other objects are attained by providing means comprising small inductors which are coupled together and respectively connected in series in pairs. These small inductors are so arranged that the degree of coupling between them may be varied without altering the effective inductance value of each pair. In this manner, the imductlve coupling between two circuits respectively including the pairs of small inductors may be varied without changing the individual circuit inductances and without the necessity for critical mechanical adjustments.

The invention will be better understood by reference to the accompanying drawing, in which:

Fig. 1 is a schematic circuit diagram of coupling means in accordance with the invention;

Fig. 2 is an elevation of one embodiment of the coupling means shown schematically in Fig. 1;

Fig; 3 is an elevation oi a modified embodiment of the coupling means shown schematically inFig. 1;

Fig.4 is an elevation of a third embodiment oi the coupling mean shown schematically in Fig. 1; and

Fig. 5 is a schematic circuit diagram of a vacuum-tube amplifier employing coupling means in accordance with the invention.

Referring to Fig. 1 of the drawing, which 5 schematically depicts the basic principle of the invention, coils I and 2 are connected in series and are coupled to coils 3 and 4 respectively,

which are also connected in series. Coils I and Coils I and 2 are connected in aiding relation,

and coils 3 and 4 are connected in opposing relation. A ferromagnetic core 5 is positioned within and is preferably coaxial with coils I, 2, 3 and 4, and is arranged to be axially movable relatively to the coils.

Ferromagnetic core 5 may be made in accordance with United States .Patent No. 1,982,689 to Polydoroff, or in a similar manner. It consists of compressed communited ferromagnetic material, and is substantially homogeneous throughout its length, the only departure from homogeneity being that which is inherent in the molding process.

In operation, the inductive coupling provided by the coupling means may be adjusted by varying the inductive coupling between coils I and 3 and between coils 2 and 4. These couplings are dependent upon the position of core 5, since the presence of the core within coils I, 3 increases the inductive coupling between these coils, and a similar result occurs when core 5 is within coils 2, 4. The minimum inductive coupling occurs when core 5 is midway between coils I, 3 and coils 2, 4, and the maximum inductive coupling is realized when core 5 is concentric'with either coils I. 3 or coils 2, 4. Core 5 is preferably slightly longer than either of coils I, 3 or coils 2, 4 and is also preferably slightly longer than the space between coils I, 3 and coils 2, 4.

As core 5 is moved into coils I, 3, the individual inductances of coils I and 3 are increased simultaneously with the increase in inductive coupling between them. At the same time however, core 5 is withdrawn from coils 2, 4. This in turn decreases the individual inductances of coils 2 and 4, by an amount which substantially compensates for the increase in the inductances of coils I and 3. Similar compensation occurs if core 5 is moved into coils 2, 4 instead of coils I, 3, but in this case the sense of the inductive coupling provided by the coupling means is reversed.

It will be understood that the desired coupling variation without change in the eifectlve inductance of coils I and 2 in series, or coils 3 and 4, also in series, is realized in accordance with the invention by the cooperation of the coils I, 3 and 2, 4 with magnetic core 5, as described above. The use of the movable core makes possible the achievement of the new result by simultaneously providing a change in the coupling between, and in the inductance of, coils I and 3 and coils 2 and 4, while maintaining substantially constant the total inductance of coils I and 2 in series and the total inductance of coils 3 and 4 in series.

Reference is now made to Fig. 2, which shows one embodiment of the adjustable coupling means of Fig. 1. Coils 8, 8 and 1, 9 are wound on insulating tube III, which is supported by members I I. Core I2 moves freely within tube It and may be actuated by handle I3, which is attached to core I2 by cementing or in other suitable manner. Connections to coils 6 and 1 in seriesaiding relation, and to coils 8 and 9 in series-opposing relation, are made to lugs I4, which are secured to members II. This embodiment is characterized by compactness and low cost of manufacture.

In the modified embodiment of Fig. 3, coils I5, I1 and I6, I8 are wound on an insulating tube It which is somewhat longer than tube II) of Fig. 2. Coils I5 and I6 are connected in series-aiding relation, and coils I1 and I 8 are connected in seriesopposing relation. Instead of a single core as in Fig 2, two shorter cores 20, 2I are employed and they are joined by means of rod 22 in such a manner that they may be simultaneously moved by handle 23. When core 20 is centered in coils I5, I1, core 2I is entirely withdrawn from coils I5, I8, and vice versa. Thus as the inductive coupling between coils I5, I1 is increased by axial movement of cores 29, 2I the inductive coupling between coils I6, I8 is simultaneously decreased, and vice versa. When the cores are midway of their travel, the inductive coupling provided by the coupling means is substantially zero, since the individual inductive couplings of coils I 5, I1 and coils I6, I8 are equal in degree and opposite in sense. The inductive coupling provided by the coupling means is a maximum when one of the cores 20, M is centered in coils I5, I1 or in coils I6, I8. Furthermore, since the inductance of one coil in each pair of series-connected coils is increased due to one of the cores 20, 2I by the same amount that the inductance of the other coil in the pair is decreased by'the other of the cores 20, 2I, the total effective inductance of coils I5, I6 in series and of coils I1, I8 in series remains substantially unchanged.

In the embodiment of Fig. 4, coil 24 consists of a universal-wound coil mounted on insulatin tube 25, and is connected in series-aiding relation with a similar coil 26. Coils 21 and 28, mounted on either side of coil 24, are connected in seriesaiding relation to form the equivalent of coil 3 of Fig. 1. Coils 29 and 30 are similarly located with respect to coil 26, and are connected in series-aiding relation to form the equivalent of coil 4 of Fig. 1. Coils 21, 28 are connected in series-opposing relation with coils 29, 30. Core 3i is axially movable to increase the inductive coupling between coils 21, 24, 28 or between coils 29, 26, 39, without appreciably altering the inductance values of coils 24, 26 in series or of coils 21, 28, 29, 39 in series, as explained above in connection with Figs. 2 and 3 of the drawing. Core 3| may be actuated by a handle 32 attached there- I shall now describe an application of my invention in the intermediate-frequency amplifier of a superheterodyne receiver. It will be understood, however, that I' do this merely to provide a iurtherillustrative embodiment of the invention, in a system well known to workers in the communication art, and that in so doing I do not limit myself to this or any other particular application of the invention, which, as to its scope and utility, is to be taken as limited only as set forth in the appended claims.

Fig. 5 of the drawing shows a vacuum-tube amplifier. The output circuit of vacuum tube 33 includes main inductor 34, coils I and 2 connected in series-aiding relation, and tuning capacitor35 to form resonant circuit I. The input circuit 01' vacuum tube 36 includes main inductor 31, coils 3 and 4 connected in series-opposing relation, and tuning capacitor 38 to form resonant circuit II. Inductors 34 and 31 may employ ferromagnetic cores, and may be so disposed with respect to each other that here is a desired degree of inductive coupling between them; or. alternatively, so that there is substantially sero inductive coupling between them. Core I is arranged to move axia within coils I, 2, 3, 4 as in Fig. 1.

- In operation, the inductive coupling. betweenresonant circuits I and II may be adjusted by varying the inductive couplings between coils I, 3 and. coils 2, 4, respectively. These couplings are dependent upon the position of core I with respect to coils I, I and 2, 4, since the presence of the core within one or the other of coils I. l and 2, 4 greatly increases the inductive coupling between them. In addition to the inductive coupling between circuits I and II due to coils I, 3 and 2, 4, there may be inductive coupling between circuits I and 11 due to the relative positions of inductors 34 and 31. Whether the inductive coupling due to coils I, 3 and 2, 4 aids or opposes the inductive coupling due to inductors I4 and 3'! depends upon which one of coils I, 3 and 2, 4 is more strongly influenced by core 5. Thus not only the degree but also the sense of the inductive coupling between the circuits I and II may be varied by axial adjustment of core 5.

The following data is given by way of illustrative example of one successful embodiment of the invention in the intermediate-frequency amplifier of a superheterodyne receiver, according to Fig. 5. A 0.34-inch tube is wound with two bifilar windings, each consisting of 21 turns of No. 36 enameled silk-covered copper wire, the windings being spaced by about two-thirds the length of a winding. The core is 0.3125 inch in diameter and 0.812 inch long, and is of the described type. With the core centered in coils I, 3, the inductance'of the coils I and 2 in series is 17.0 microhenries, the inductance of coils I and 4 in series is 19.2 microhenries, and the mutual inductance between coils I and 2 in series and coils 3 and 4 in series is 11.3 microhenries. With the .core centered in coils 2, 4, the inductance of coils I and 2 in series is 16.0 microhenries, the inductance of coils l and 4 in series is 19.5 microhenries, and the mutual inductance between coils I and 2 in series and coils 3 and 4 in series is 10.0

microhenries,

Inductors 34 and 31 are each 1.0 millihenry, and the change in the total inductance of either circuit, due to motion of the core to adjust the coupling between the circuits, is therefore only 0.1 percent, which is negligible. The change in inductance may be made even less, however, by a slight changein the number of turns in one or more of the coils. V

The measured Q of resonant circuit I or II by itself is 168, and becomes 153 upon introducing coils I and 2 or coils I and 4 into the circuit bein series is. zero. The maximum coupling which is available between circuits I and II is 1.78 percent under these conditions. The coupling between circuits I and 11 may be brought to zero by suitable adjustment of the core. It will be understoodthat the value of critical coupling will be somewhat greaterthan above stated when the coupling device is associated with'vacuum tubes in an amplifier.

Thus in the example above described, it is possible to increase the inductive coupling considerahly beyond the critical value to obtain a desired overcoupled condition. This is sufllcient to provide the necessary broadening of the selectivity characteristic of the coupling device in most instances. It still higher degrees of inductive coupling are required, they are readiLv obtained by providing coils I, I and 2, 4 with additional turns.

As will be apparent to those skilled in the electrical arts, my invention has advantageous application to numerous problems in electrical circult design. Its applications inthe communication art, and particularly in the high-frequency and radio branches of that art, are of especial importance, since it is in this field that alterations in the performance of networks between which it is desired to utilize a variable coupling become more troublesome. By way of additional illustrative examples of particular systems in this pling may be actuated by the tuning control in.

such a way as to produce any desired relation between the resonant frequencies of the circuits and the coupling between them. The invention may also be advantageously utilized to provide a variable regenerative -or degenerative coupling between the plate circuit and the grid circuit of a thermionic tube, or between an antenna or pick-up system and the first resonant circuit in a radio receiver.

In oscillators, signal generators and the like, my invention may be employed to provide a variable attenuation between wide limits of the oscillation or signal delivered to the output terminals or the load circuit.

Other advantageous applications of the inven tion will readily occur to those skilled in the art, as well'as various modifications of the structures here shown and described by way of illustrative example of successful embodiments. Such applications and modifications are within the scope of the invention, as set forth in the appended claims.

Having thus described my invention, what I claim is:

1. A high-frequency system including two res,- onant circuits each containing an inductance,

and a variable coupler'between said circuits comprising two pairs of coils non-inductively related to said inductances but inductively related to each other, and a ferromagnetic core movable relatively to said pairs of coils, the coils in each of said pairs being so related that said variable coupler adds a substantially unvarying inductance value in cache! said circuits.

2. A selective high-frequency system compris ing a pair of resonant circuits each including an inductance, and means for variably coupling said circuits including two aidlngly related coupling coils in a first of said circuits, two opposingiy related coupling coils in the second of said circuits, and a ferromagnetic core movable relatively'to said coupling coils, said coupling coils being noninductively related to said inductances.

3. A high-frequency band-pass system including two resonant circuits each having an inductance, means for adjusting said circuits to desired resonant frequencies, and means for varying the h width of the band of frequencies passed by said "-system comprising two aidingly related coils in p a first of said circuits, two opposingly related coils in the second of said circuits, and a ferromagnetic core movable relatively to said coils, said coils being non-inductively related to said in- -ductances.

" in a first of said circuits, plural opposingly related coupling coils in a second of said circuits, and a ferromagnetic core movable relatively to said coils, said core and said coils being so related that movement of said core relatively to ;:said coils varies the inductive coupling between said circuits while maintaining the total effective inductance in each of said circuits substantially constant. a

5. A selective high-frequency system comprising a pair of resonant circuits each having an inductance, and means for variably coupling said circuits including two aidinglyrelated coupling coils in a first of said circuits, two opposingly related coupling coils in the second of said circuits, and a ferromagnetic core movable relatively 'to.

said coils and said core being so arranged and disposed that movement of said core relatively to said coils varies the coupling between the coils in the first of said circuits and the coils in the second of said circuits while maintaining the effective inductance of the coils in each of said circuits substantially constant.

'7. In a high-frequency band-pass system including two resonant circuits, means for adlusting said circuits to a desired resonant frequency, and means for varying the width 01 the band of frequencies passed by saidcircuits while maintaining said resonant frequency substantially unchanged comprising plural coupling coils in each of said circuits and a ferromagnetic core movable relatively to said coils, said coils and said core being so arranged and disposed that movement of said core relatively to said coils varies the coupling between the coils in the first of said circuits and the coils in the second of said circuits while maintaining the eflfective inductance of the coils in each of said circuits substantially constant.

8. In a selective high-frequency system including a pair of resonant circuits each having an inductor and a capacitor, two coupling coils connected mutually in series and in series with the inductor and the capacitor in each of said circuits, the two coils in the first of said circuits being coaxially arranged at the ends or an insulating tube and wound in aiding relation, the two coils in the second of said circuits being respectively disposed closely adjacent the two coils in the first of said circuits and being wound in opposing relation, and a ferromagnetic core disposed within said tube and movable relatively to said coils to vary the inductive coupling between said circuits while maintaining the total effective inductance in each of said circuits substantially constant. v

9. In a selective high-frequency system including first and second resonant'circuits each having inductance and capacitance and having coupling therebetween, 'means for providing additional inductive coupling between said circuits and for varying the degree and controlling the sense of said additional inductive coupling relatively to said first-mentioned coupling, while maintaining the total effective inductance in each of said circuits substantially constant, comprisin'g first and second windings respectively in series with the inductance and capacitance in said first and second circuits and each having two coils, the coils of said first winding being connected in series-aiding relation, the coils of said second winding being connected in seriesopposing relation, the first coils of said windings and the second coils of said windings being arranged closely adjacent in pairs wound in spaced ALFRED CROSSLEY. 

